1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display panel using a gray tone mask.
2. Description of the Background Art
Liquid crystal display (LCD) technology has been developing rapidly. It is used for most portable electronic devices due to its light weight. As its application range is enlarged, manufacturing technology with reduced cost and excellent productivity is required.
An LCD is made by depositing or coating a plurality of thin films and patterning by a photolithography process. The number of photo-masks used for manufacturing an LCD is a measure of process simplification. One cycle of photolithography is processed with one mask. Many researchers have studied the possible reduction of masks utilized, since to reduce only one photo-mask step could considerably reduce the manufacturing cost.
Generally, as shown in FIG. 2, an LCD comprises a color filter panel 30, an active panel 10 and liquid crystal 22 disposed between the two panels 10 and 30. Polarizing film 11 and 31 for the linear-polarizing of visible rays are mounted on the respective outer surfaces of the two panels 10 and 30. On one surface of the color filter panel 30 the polarizing film 31 is mounted and on the other surface a color filter 32 and common electrode 33 are formed. The polarizing film 11 is mounted on one surface of the active panel 10 and on the other surface a plurality of bus lines 12, a plurality of data bus line 13, a switching device A and a pixel electrode 16 are formed.
The structure of the active panel 10 will be described with reference to the schematic value shown in FIG. 2. The active panel 10 comprises a plurality of gate bus lines 12, gate bus line pad 12b, a plurality of data bus lines 13, data bus line pad 13b, switching device A and a pixel electrode. The plurality of gate bus lines 12 are parallel to each other and the plurality of data bus lines 13 cross the plurality of gate bus line 12 thus forming a matrix structure. In the area formed by the gate bus line 12 and data bus line 13, which cross each other, a TFT switching device which comprises a gate electrode 12a branched from the gate bus line 12, a source electrode 13a branched from the data bus line 13, and a drain electrode 13c opposed to the source electrode 13a, is positioned. The pixel electrode 16 is connected, through electrical contact with a hole 15, to the drain electrode 13c which is an output terminal of the switching device A.
The manufacturing process of the active panel of the above LCD apparatus will be described with reference to FIGS. 3A to 3G showing the manufacturing process of the section line a—a of FIG. 2 and FIGS. 4A to 4F showing the manufacturing process of the section line b—b of FIG. 2.
A first metal layer is formed on a transparent substrate such as a glass by depositing thereon one of aluminum and aluminum-based alloys (Al—Pd, Al—Si, Al—Si—Ti, Al—Si—Cu and the like). The plurality of gate bus lines 12, gate electrode 12a and the like are formed on the transparent substrate 11 by patterning the first metal layer using a first mask (FIGS. 3A and 4A).
An insulating layer 17′ is formed using SiNx or SiOx which have an excellent interfacial characteristic and a high endurance voltage on the substrate including the plurality of gate bus lines 12 and gate electrode 12a thereon. On the insulating layer 17′, intrinsic semiconductor material 18′ such as amorphous silicon (a-Si) and extrinsic semiconductor substance 19′ are deposited sequentially (FIGS. 3B and 4B).
A gate insulator 17, intrinsic semiconductor layer 18 and an extrinsic semiconductor layer (19) (ohmic contact layer) are formed by patterning the insulating layer 17′, the intrinsic semiconductor material 18′ and the extrinsic semiconductor 19′ using a second mask (FIGS. 3C and 4C).
A second metal layer is formed on the substrate including the gate insulator 17, the intrinsic semiconductor layer 18 and the extrinsic semiconductor layer 19 by depositing thereon one of aluminum and aluminum-based alloys (Al—Pd, Al—Si, Al—Si—Ti, Al—Si—Cu and the like). Next, the plurality of data bus lines vertical to the above gate bus line 12 and the source electrode 13a branched from the data bus line 13 are formed by patterning the second metal layer using a third mask. Then, a drain electrode 13c for functioning as an output terminal in the position opposed to the source electrode 13A are formed (FIGS. 3D and 4D). The gate insulator 17, intrinsic semiconductor layer 18 and extrinsic semiconductor layer 19 are formed with the same width as that of the data bus line 13 and act as a buffer layer.
Next, a protecting film 20 is formed on the substrate including the gate bus line 12, data bus line 13, gate electrode 12a, semiconductor layers 18 and 19, source electrode 13a and the drain electrode 13c by coating with an insulating material such as SiNx or SiOx and the like (FIGS. 3E and 4E).
A contact hole 15 is formed by removing part of the protecting film 20 using a fourth mask (FIG. 3F) so that a part of the drain electrode 13c which is the output terminal of the switching device and positioned below the protecting film 20 can be exposed.
An Indium Tin Oxide (ITO) film is deposited on the entire surface of the substrate by sputtering. Then the ITO film is etched in a certain pattern using a fifth mask. Due to the formation of the ITO film pattern, a pixel electrode 16 is contacted with the drain electrode 13c which is the output terminal of the switching device through the contact hole 15 (FIGS. 3G and 4F). By the above respective processes, an active panel portion of a LCD are manufactured.
In the above manufacturing method, a TFT of an active panel is manufactured using 5 masks. Recently, efforts have been made to simplify the manufacturing process and the necessity for core technology capable of manufacturing a TFT using just 4 masks has been discussed.